1. Technical Field
The present invention relates to a deterministic quantum emitter operating at room temperature in an optical communication wavelength using the intersubband transition of a nitride-based semiconductor quantum dot, a method of fabricating the same, and an operating method thereof and, more particularly, to a deterministic quantum emitter operating at room temperature (300 K) or more while having a communication wavelength band of about 1.55 μm using the intersubband transition of a nitride-based semiconductor quantum dot, a technology for fabricating the deterministic quantum emitter, and an operating technology thereof.
2. Description of the Related Art
As the information communication technology is advanced, the importance of security is increased. The need for the development of quantum information communication that cannot be hacked owing to the non-cloning theorem of quantum and separation indivisibility, that is, characteristics of a quantum emitter, is increasing.
Information processing and calculation using the existing current signal has implemented a high degree of integration and calculation speed owing to the development of the process technology, but shows its limits due to a heating problem in an electronic device and a quantum-mechanical effect in a nanometer level as the amount of information processing is increased. Accordingly, the development of an information processing method using light in order to solve the heating problem in the information processing process is in progress. A demand for a quantum emitter capable of implementing a quantum physical phenomenon in optical communication are increasing as one method for overcoming the limits of the information communication field based on a traditional physical phenomenon.
A spontaneous parametric down conversion (SPDC) method is now used as one of multiple quantum emitters and is widely used in quantum optics research or quantum information experiments. This method may be used for quantum logic operation based on a quantum entanglement phenomenon in which lights generates two photons having a quantum entanglement relation while passing through nonlinear crystals. However, this method additionally requires a process of checking a heralded single photon in order for this method to be used in a clock-based system because photons are generated probabilistically based on the nonlinear process.
Accordingly, a related system is complicated, and an operation number is relatively reduced because photons are consumed to check the heralded single photon. Furthermore, this method has a principle limit that the operation number must be reduced for the accuracy of operation because there is a tradeoff between purity and brightness for a single photon state. Accordingly, a corresponding quantum emitter can operate at room temperature and has a wavelength of 1.55 μm, but has a limited operation speed due to the principle of probabilistic production of photons.
As an example of multiple quantum emitters, research related to quantum information communication in which the intensity of a laser having a pulse form in time is extremely reduced so that the original photon state of the laser has a physical state closer to a single photon state is in progress. However, such a quantum emitter has the same problem as the SPDC because a single photon is present with low probability per pulse. Accordingly, a semiconductor quantum dot using a thin film deposition method is being developed as a candidate capable of solving the problem in that photons are formed stochastically.
The semiconductor quantum dot means a semiconductor system having a three-dimensional (3-D) quantum confinement effect and may be used as a quantum emitter because an energy level has a discontinuous characteristic due to the 3-D quantum confinement effect.
A semiconductor quantum dot using the thin film deposition method may be used for a clock-based quantum system because a self-emissive process of photons is determined with respect to energy excitation in an ideal case. Furthermore, the semiconductor quantum dot has an advantage in that current driving is possible by forming an electrode because the semiconductor quantum dot is a semiconductor and can be doped in principle. Accordingly, a quantum emitter can become an element using the semiconductor quantum dot and may be commercialized. Furthermore, in general, the size of a semiconductor quantum dot is about 20 nm or less. If such semiconductor quantum dots are homogeneously fabricated using the thin film deposition method, quantum emitters can be mass-produced in a wafer scale.
In order to fabricate a semiconductor quantum dot emitting in a communication wavelength area, the strain relaxation mechanism of a crystalline structure using a III-As semiconductor compound is applied using molecular beam epitaxy (MBE), that is, one of thin film deposition methods. On March, 2016, there was reported that the execution capability of the SPDC method used as the existing quantum emitter was exceeded using the semiconductor quantum dot of the above type. Furthermore, a quantum key distribution, that is, a kind of quantum password, has been implemented up to 120 km using the semiconductor quantum dot of the above type. However, the mass production of the quantum emitter is limited because the semiconductor quantum dot requires an ultra low temperature of 4 K, that is, a liquid helium cooling temperature, in order for the semiconductor quantum dot to operate as the quantum emitter. Furthermore, in terms of III-As material properties using inter-band transition, that is, transition between emittable energy levels, a quantum confinement effect of holes cannot be implemented as a temperature is closer to room temperature because atoms do not have a high band offset. Accordingly, there is no room to improve a problem of an operation at room temperature.
In the present optical communication wavelength band, an example in which an operation issue at room temperature has been solved has not yet been reported regarding a quantum emitter having the smallest optical loss of 1.55 μm. In order for quantum optical communication to be advanced in the future, it is expected that the existing well-established optical communication networks will be applied using a plurality of optical channels (i.e., quantum emitters). Accordingly, the need for a technology capable of fabricating a quantum emitter capable of operating at room temperature in an optical communication wavelength band is increasing.
Korean Patent No. 10-1012265 relates to a method of fabricating a single carrier device operating at room temperature, and describes a technology relating to a single carrier device operating at room temperature using a plurality of silicide metal points formed in series as multiple quantum dots and a method of fabricating the same. The conventional patent is a technology relating to an electrical device using before-and after-capturing of a single carrier as an electrical signal of 0 and 1, and is different from a technology in which a nitride-based semiconductor quantum dot is used as an optical signal generator.